fs storage

game/internal/repo/fs/fs.go

@@ -0,0 +1,222 @@
+package fs
+
+import (
+	"encoding"
+	"errors"
+	"fmt"
+	"galaxy/util"
+	"math/big"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+const (
+	defaultPerm   = 0o644
+	lockFile      = ".lock"
+	oldFileSuffix = ".old"
+	newFileSuffix = ".new"
+)
+
+type fs struct {
+	root string
+	lock *os.File
+}
+
+func NewFileStorage(path string) (*fs, error) {
+	filepath.Join("", "")
+	absPath, err := filepath.Abs(path)
+	if err != nil {
+		return nil, fmt.Errorf("path %s invalid: %s", path, err)
+	}
+	if ok, err := util.DirExists(absPath); err != nil {
+		return nil, fmt.Errorf("check dir exist: %s", err)
+	} else if !ok {
+		return nil, errors.New("directory does not exist: " + absPath)
+	}
+
+	if ok, err := util.Writable(absPath); err != nil {
+		return nil, fmt.Errorf("check dir access: %s", err)
+	} else if !ok {
+		return nil, errors.New("directory should have read-write access: " + absPath)
+	}
+
+	fs := &fs{
+		root: path,
+	}
+	return fs, nil
+}
+
+func (f *fs) Lock() (func() error, error) {
+	lockPath := f.lockFilePath()
+	exists, err := util.FileExists(lockPath)
+	if err != nil {
+		return nil, fmt.Errorf("check lock file exists: %s", err)
+	}
+	if exists {
+		return nil, errors.New("lock file already exists")
+	}
+	fd, err := os.OpenFile(lockPath, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("create lock file: %s", err)
+	}
+	f.lock = fd
+	unlock := func() error {
+		if err := f.lock.Close(); err != nil {
+			return fmt.Errorf("close lock file: %s", err)
+		}
+		if err := os.Remove(f.lock.Name()); err != nil {
+			return fmt.Errorf("remove lock file: %s", err)
+		}
+		f.lock = nil
+		return nil
+	}
+	if _, err := f.lock.Write(big.NewInt(time.Now().UnixMilli()).Bytes()); err != nil {
+		return nil, errors.Join(fmt.Errorf("write lock file: %s", err), unlock())
+	}
+	return unlock, nil
+}
+
+func (f *fs) Exists(path string) (bool, error) {
+	return util.FileExists(filepath.Join(f.root, path))
+}
+
+func (f *fs) WriteSafe(path string, v encoding.BinaryMarshaler) error {
+	if v == nil {
+		return errors.New("cant't marshal from nil object")
+	}
+
+	targetFilePath := filepath.Join(f.root, path)
+	if targetFilePath == f.lockFilePath() {
+		return errors.New("can't write to the lock file")
+	}
+
+	data, err := v.MarshalBinary()
+	if err != nil {
+		return fmt.Errorf("marshal data: %s", err)
+	}
+
+	targetDir := filepath.Dir(targetFilePath)
+	if targetDir != f.root {
+		ok, err := util.DirExists(targetDir)
+		if err != nil {
+			return fmt.Errorf("check target dir exists: %s", err)
+		}
+		if !ok {
+			err := os.MkdirAll(targetDir, os.ModePerm)
+			if err != nil {
+				return fmt.Errorf("create target dirs: %s", err)
+			}
+		}
+	}
+	oldFilePath := targetFilePath + oldFileSuffix
+
+	targetExists, err := util.FileExists(targetFilePath)
+	if err != nil {
+		return fmt.Errorf("check target file exists: %s", err)
+	}
+	if targetExists {
+		oldFileExists, err := util.FileExists(oldFilePath)
+		if err != nil {
+			return fmt.Errorf("check old file exists: %s", err)
+		}
+		if oldFileExists {
+			return fmt.Errorf("old file exists at: %s", oldFilePath)
+		}
+	}
+
+	newFilePath := targetFilePath + newFileSuffix
+	newFileExists, err := util.FileExists(newFilePath)
+	if err != nil {
+		return fmt.Errorf("check new file exists: %s", err)
+	}
+	if newFileExists {
+		return fmt.Errorf("new file exists at: %s", oldFilePath)
+	}
+
+	err = os.WriteFile(newFilePath, data, defaultPerm)
+	if err != nil {
+		return fmt.Errorf("write data to the new file: %s", err)
+	}
+
+	if targetExists {
+		if err := os.Rename(targetFilePath, oldFilePath); err != nil {
+			return fmt.Errorf("rename target file to the old file: %s", err)
+		}
+	}
+
+	if err := os.Rename(newFilePath, targetFilePath); err != nil {
+		return fmt.Errorf("rename new file to the target file: %s", err)
+	}
+
+	if targetExists {
+		err := os.Remove(oldFilePath)
+		if err != nil {
+			return fmt.Errorf("remove old file: %s", err)
+		}
+	}
+	return nil
+}
+
+func (f *fs) Write(path string, v encoding.BinaryMarshaler) error {
+	if f.lock == nil {
+		return errors.New("lock must be acquired before write")
+	}
+
+	return f.WriteSafe(path, v)
+}
+
+func (f *fs) Read(path string, v encoding.BinaryUnmarshaler) error {
+	if f.lock == nil {
+		return errors.New("lock must be acquired before read")
+	}
+
+	return f.readUnsafe(path, v)
+}
+
+func (f *fs) ReadSafe(path string, v encoding.BinaryUnmarshaler) error {
+	if f.lock != nil {
+		timeout := time.NewTimer(time.Millisecond * 100)
+		checker := time.NewTicker(time.Millisecond)
+	out:
+		for {
+			select {
+			case <-checker.C:
+				if f.lock == nil {
+					checker.Stop()
+					timeout.Stop()
+					break out
+				}
+			case <-timeout.C:
+				checker.Stop()
+				return errors.New("timeout waiting for lock release")
+			}
+		}
+	}
+
+	return f.readUnsafe(path, v)
+}
+
+// readUnsafe reads the file contents without locking mechanism in mind.
+// Using readUnsafe directly may cause errors if file being written at the moment.
+func (f *fs) readUnsafe(file string, v encoding.BinaryUnmarshaler) error {
+	if v == nil {
+		return errors.New("can't unmarshal to a nil object")
+	}
+
+	targetFilePath := filepath.Join(f.root, file)
+	if targetFilePath == f.lockFilePath() {
+		return errors.New("can't read from the lock file")
+	}
+
+	data, err := os.ReadFile(targetFilePath)
+	if err != nil {
+		return fmt.Errorf("reading data file: %s", err)
+	}
+
+	return v.UnmarshalBinary(data)
+}
+
+func (f *fs) lockFilePath() string {
+	return filepath.Join(f.root, lockFile)
+}